Tank trailers are well known for transporting dry bulk materials. By way of example, a tank trailer may be used to transport dry bulk materials from a rail car to a raw material processing plant or a manufacturing facility. The tank trailer is typically attached to a tank truck (also commonly referred to as a “tank tractor”) to transport the tank trailer from the rail car to the processing plant or the manufacturing facility. In some instances, a blower mounted on the tank truck is used to unload (also commonly referred to as “discharge” or “off-load”) the dry bulk material from the tank trailer into a storage container at the processing plant or manufacturing facility. The blower may also be operated as a vacuum to load the dry bulk material from the rail car into the tank trailer. However, the operator must take care that the blower is not operated beyond its maximum vacuum capacity, which could lead to an overheating condition and eventually result in a total failure of the blower.
By way of example, a blower assembly including a blower, a blower muffler and a blower filter are mounted on the tank truck. A dry bulk material tank and a trailer filter are provided on the tank trailer. The blower assembly on tank truck is connected in pneumatic (i.e., air) communication with the trailer filter on the tank trailer through one or more flexible hoses and/or rigid conduits. When the blower is operated as a vacuum to load dry bulk material into the dry bulk material tank of the tank trailer, air is pulled through the blower filter and discharged to atmosphere through an outlet port provided on the blower muffler. The air is further pulled from the trailer filter through the hoses and/or conduits that connect the blower assembly to the trailer filter. The trailer filter is likewise in pneumatic (i.e., air) communication with the interior of the dry bulk material tank on the tank trailer through at least one flexible hose and/or rigid conduit. The air is further pulled from the interior of the dry bulk material tank on the tank trailer through the hose and/or conduit to the trailer filter. Thus, a vacuum is created within the fry bulk material tank to load the tank trailer with dry bulk material from, for example, a rail car connected to the tank of the tank trailer by at least one flexible hose and/or rigid conduit.
A serious problem can occur if the dry bulk material being loaded into the tank trailer is carried into the vacuum filter. The trailer filter may clog and prevent air from flowing freely from the trailer filter to the blower assembly on the tank truck. In some cases, for example if the trailer filter is damaged, the dry bulk material may pass through the trailer filter and be carried to the blower filter. In either event, the blower may become starved of air at the suction line between the blower and the blower filter, and consequently, operate beyond its maximum vacuum capacity. When the blower is operated beyond its maximum vacuum capacity for an excessive period of time it can overheat and cause internal contact between its moving parts, which typically results in a total failure of the blower. A total failure of the blower requires a time-consuming, and thus costly, replacement of the blower on the tank truck. The tank trailer may be provided with a vacuum gauge positioned at a convenient location on the tank trailer for monitoring the vacuum pressure at the trailer filter. However, no indication is given to the operator that the blower is being starved of air at the suction port if either the trailer filter or the blower filter is clogged, or there is some other restriction in the connecting hoses and/or conduits, such as a closed valve.